Answer:

CSMA:

CSMA stands for Carrier Sense Multiple Access. It is a Media Access Control protocol that is used to control the flow of data in a transmission media so that packets do not get lost and data purity is preserved. There are two modifications to CSMA that are the CSMA CD (Collision Detection) and CSMA CA (Collision Avoidance) where each modification having its own strengths.

The difference between CSMA/CD and CSMA/CA are shown below:

1. CSMA/CD takes effect after a collision while CSMA CA takes effect before a collision.
2. CSMA CD only minimizes the recovery time while CSMA/CA trims the possibility of a collision.
3. CSMA/CD is commonly used in wired networks while CSMA/CA is used in wireless networks.

CSMA-CD not used in WLAN because of two main reasons that shown below:

• Implementing a collision detection procedure would need the implementation of a full duplex radio capable of transmitting and receiving at the same time, an approach that would increase the cost powerfully.
• In a wireless environment we cannot assume that all stations hear each other and the fact that a station wants to transmit and senses the medium where the medium is free around the receiver area.

To overcome these difficulties, CSMA-CA mechanism can be used in the place of collision detection (CSMA-CD) mechanism. CSMA-CA is used on wireless networks. CSMA-CA doesn’t detect collisions but quite avoids them through the use of a control message. The control message collides with another control message from another node, it means that the medium is not available for transmission and the back-off algorithm needs to be applied before attempting retransmission.